The zero field cooled (\(ZFC\) ) state of the canonical spin-glasses has been investigated with various macroscopic as well as microscopic experimental techniques like dc magnetization, ac susceptibility, specific heat, neutron scattering, M\(\ddot{o}\) sbauer spectroscopy, muon spin resonance studies, etc. [1]}, [2]}, [3]}. This \(ZFC\)  state is found to be a non-equilibrium state with time and history dependent properties [1]}, [2]}, [3]}. These interesting physical properties are understood within the mean-field theoretical framework involving Parisi’s solution of the infinite-range Sherrington-Kirkpatrick (SK) model that predicts a thermodynamic second-order phase transition from the high-temperature paramagnetic state to the low-temperature spin-glass state [7]}, [8]}. Within the same theoretical framework, cooling the system
in the presence of a finite magnetic field from a paramagnetic state would bring the spin-glass to an “infinite time equilibrium state” [1]}, [2]}, [3]}. This is the field cooled (\(FC\) ) state of spin-glass, and it is widely believed to be an equilibrium state of the system. However, in recent times we have shown that the \(FC\)  state in dilute canonical spin-glass systems like AuMn(1.8%) and AgMn(1.1%) alloys is not really an equilibrium state of the system [12]}, [13]}. The \(FC\)  state of these canonical spin-glasses clearly shows the well-known magnetic memory effect in dc magnetization studies and frequency dependence in ac-susceptibility measurements [12]}, [13]}.
